The present invention relates to a method for making a record stylus for use in reproducing signals from a capacitance record and to the stylus manufactured by the method, and in particular to a method for forming an electrode on a surface of a diamond body.
Pickup styluses for use with capacitance disk records comprise a diamond body and an electrode attached thereto to read an information signal from each track of the record by sensing its geometric surface variations as variations is capacitance. The electrode is conventionally formed by vacuum deposition, sputtering, or ion plating a conductive material such as hafnium or titanium. Since such conductive material is chemically different from the underlying material, the electrode is only physically attached to the underlying body, resulting in an electrode having a tendency to separate therefrom during use due to friction with the record surface. Another conventional method involves ion implantation. However, due to the strong bonding between carbon atoms that constitute the diamond, it is difficult to inject a sufficient amount of ions to provide a conductive layer.
Another problem arises from the fact that the stylus has a tendency to swing, or pitch as it moves along the track and this causes the electrode to frictionally contact with the record surface at an angle thereto so that the lowermost end of the electrode is partially lost by the friction.
Co-pending U.S. patent application Ser. No. 268,888 filed June 1, 1981 now U.S. Pat. No. 4,409,712 issued Oct. 18, 1983 and assigned to the same assignee as the present invention, discloses a method whereby a diamond body is heated in a virtual vacuum or an inert-gas containing environment with a small amount of oxygen to convert the carbon molecules of the surface area into a layer of conductive carbon to serve as the electrode. Since the conductive carbon layer is integral with the diamond body, the electrode is not separable therefrom and is resistant to wear.
However, the prior method has an inherent difficulty in forming the diamond body into the desired shape and dimensions suitable for a pickup stylus. Since the electrode is usually formed in a process prior to the shaping process, the surface of the diamond body is entirely surrounded by the conductive layer of which a substantial portion must be removed to form the electrode. Since the conductive carbon layer is formed integrally with the underlying diamond body, it is a time-consuming affair to remove the conductive carbon layer.